This application is a 371 of PCT/EP99/03221 filed May 11, 1999.
The present invention generally relates to vehicle braking systems and more particularly relates to a hydraulic brake system for controlled and comfortable braking operations.
Hydraulic brake systems are increasingly equipped with devices which permit performing also independently controlled comfortable braking operations. In contrast to a controlled braking operation effected by a driver, which is generally related to traction and/or brake slip control, comfort braking is activated by a cruise control system, for example. One problem encountered in this matter, however, is that such a comfort braking operation must be carried out with a controlled brake force because otherwise the cruise control system cannot be operated with a sufficient rate of accuracy and continuity.
In view of the above, an object of the present invention is to provide a hydraulic brake system of the type mentioned hereinabove which allows applying a brake pressure that is continuously controllable in small steps for conducting comfortable braking operations.
The present invention includes an analog valve and a hydraulic pump both of which are adapted to be actuated by a control device in such a manner that the brake pressure for comfort braking can be increased or decreased in an essentially continuously variable manner.
In a preferred embodiment, the valve assembly is configured as an analog three-way valve provided for each wheel brake, the inlets of the valve being connected to the pressure side of the hydraulic pump, and the first outlet thereof being respectively connected to a wheel brake and the second outlets thereof being connected to a low-pressure side of the brake system, wherein the three-way valves and the hydraulic pump are actuatable by a control device to such effect that the brake pressure for a comfortable braking operation can be increased or decreased in an essentially continuously variable manner.